1. Field of the Invention
The present invention relates to a method for producing an electric iron sheet, more particularly a non-oriented iron sheet containing no more than 3.5% silicon, and when containing said silicon, it is present in a stable form.
2. Description of the Prior Art
Among electric iron sheets as soft magnetic materials there are the following kinds: a grain oriented silicon steel sheet, which is composed of a recrystallized collective texture crystallographyically expressed as (110) [001] and has the (110) plane on the rolling plane and a [001] orientation arranged in the rolling direction; a non-oriented silicon steel sheet having a recrystallized texture, in which the orientation does not come into question; and an extremely low carbon magnetic material containing no silicon or a very small amount thereof. These electric sheets are used as iron cores for electric devices and the like in accordance with their respective properties.
For instance, a grain oriented silicon steel sheet is widely used for transformers and large capacity electromotors, because it has excellent magnetic properties, because it is very easily magnetizable in the rolling direction, that is, in the [001] orientation; the core loss value is very low and the permeability is high. On the other hand, a non-oriented silicon steel sheet is used for small-sized electro-motors, relays and the like, because a processing of high efficiency can be carried out on account of its good workability, though it is somewhat inferior to the grain oriented silicon steel sheet in magnetic properties. Further, an extremely low carbon magnetic material is widely used for small-sized direct current electro-motors, electro-motors for household electric devices and the like, because it has adequate magnetic properties and is low in production cost.
In general, in the case of a so-called extremely low carbon magnetic material, in which the silicon content is below 2%, Al is added in order to improve the magnetic properties. This is to effect the improvement of magnetic properties by causing AlN to precipitate, but the effective amount of Al to be added should be more than 0.1%.
Consequently, because of the need to add Al in the amount previously mentioned, the production of an extremely low carbon magnetic material possessing the required magnetic properties is expensive and its cost is expected to rise. On the other hand, in the case of an extremely low carbon magnetic material, when the Al content is less than 0.1%, the precipitation temperature of AlN becomes lower, the precipitates become fine and the core loss is remarkably deteriorated.